The present invention relates generally to the field of thread rolling dies and in particular to a boltmaker style flat die for forming threads on a cylindrical fastener blank.
Thread rolling dies are a known means for rolling a thread form on bolts, studs, etc., and are generally rectangular plate members having one surface thereon serrated. These serrations include alternate ridges and grooves, which conform in plan to the shape of the screw threads to be rolled. The serrations run the length of the die face and are inclined with respect to the longitudinal axis of the die face at an angle corresponding to the lead angle of the threads to be rolled. The dies are used in mating pairs with their serrated faces facing each other. A cylindrical blank of the bolt to be threaded is placed between the dies at one end thereof. The dies are then pressed against the shank portion of the blank and one of the dies is moved longitudinally, thereby rotating the blank about its axis and roll forming the screw threads thereon.
Boltmaker style thread rolling dies known in the art usually have a start, which is a chamfer with depth equivalent to thread depth, and a ramp region on the die to permit the die to penetrate the cylindrical blank at a controlled rate until full depth is reached. These dies also have a dwell portion, which is normally one-half the length of the die, to provide an "ironing out" action or smoothing operation that develops the full depth of the threads. Additionally, these dies usually have a roll-off section which permits the gradual loss of contact between the die and screw, without marking the finished workpiece. Dies of this type have been used in the past to roll single thread forms on cylindrical blanks and have been found to be a relatively fast and efficient method of forming threaded members. However, large rolling forces to which the dies are subjected during the thread forming process, thereby resulting in reduced die life.
Accordingly, it is a general object of the present invention to provide thread rolling dies which overcome the disadvantages of the prior art. It is a further object of the present invention to provide thread rolling dies which have a longer tool life with minimal cost increase. A still further object of the present invention is to provide thread rolling dies that are simple and durable in construction, economical to manufacture, and highly efficient in operation.